Chainsaw Repair

cs-600p carb has the pass through - semi fixed jet in the metering chamber.  If the check valve in that jet is bad, Echo wants you to buy a new carb.  The workaround is the Husky HDA-199 uses the same semi fixed jet, and walbro sells it through their parts distribution system.

86-578-1 Nozzle Assembly

The repair procedure is to strip the carb down, warm up the casting and press the bad jet into the throttle bore.  Use a light hammer and a 1/8 punch.  Tap the new jet in from the metering chamber while the casting is warm.       

For tuning its best to keep the engine under a load and off the rpm limiter to set the high side.  Otherwise, use a tach.